The present invention relates to an improved process for the production of carboxymethylated alcohols or phenols, and in particular, of polyether alcohols.
The carboxymethylated alcohols and ether alcohols are compounds of the type R(OCH.sub.2 CH.sub.2).sub.n --X--CH.sub.2 COOH which, X=O, S with appropriate selection of the residue R and of the degree of oxethylation n, represent valuable tensides (surface active agents) usable, for example, in tertiary oil recovery. (See, e.g., Tenside Detergents 16:256-261 [1979], whose disclosure is incorporated by reference herein).
A conventional method for the preparation of etheric carboxylic acids or polyether carboxylic acids comprises first obtaining the corresponding alcoholates from an alcohol or ether alcohol, respectively, and an alkali metal hydroxide, and thereafter carboxymethylating these products with sodium chloroacetate (See, e.g., U.S. Pat. No. 2,623,900). A substantial improvement in this process has been disclosed in more recent literature. According to U.S. Pat. No. 3,992,443, the polyether alcohol is mixed with sodium chloroacetate and an equivalent amount of sodium hydroxide is added to this mixture either in the form of a powder or as an aqueous, approximately 50% strength solution; in the latter case, the water introduced is simultaneously removed from the reaction mixture as exhaustively as possible (cf. Example 5 thereof).
A very similar mode of operation is disclosed in Japanese Patent Application No. Sho-50-24 215 of Kao Sekken K.K.
In both literature references, the attainable degree of conversion to the correspondingly carboxymethylated compounds is indicated as about 90 molar percent if the process is carried out with a molar ratio of oxethylate:chloroacetate of 1:1. (See U.S. Pat. No. 3,992,443, Example 5; and No. Sho-50-24 215, Examples 1 and 2.) If still higher degrees of conversion are demanded, this can only be attained by using a considerable excess (20-50%) of chloroacetate as compared with the alcohol or ether alcohol (see U.S. Pat. No. 3,992,443, column 3, lines 1-6). In Example 11 of this patent, a total of 2.25 moles of sodium chloroacetate is used per 1.5 moles of oxethylate, to obtain a degree of conversion of 98.6% into the desired carboxylic acid. In addition, another drawback involves the long reaction period of about 36 hours required to reach this degree of conversion.